1. Field of the Invention
The present invention relates to an interface device for interfacing between a networkable device and a network, and particularly relates to such an interface device which is controllable to isolate the network from the networkable device.
2. Description of the Related Art
One desirable characteristic of networkable devices is the capability to upgrade the device so as to provide enhanced performance or extended and new functionality. For example, in connection with previously deployed legacy devices such as network printers, it is advantageous to be able to upgrade functionality of the printer so as to provide extended functionality not originally provided with the printer (such as printing of gray-scale images) or to provide improvements in performance (such as more efficient print engines).
Conventionally, such upgrades are provided through re-programming of firmware included with the legacy device. Existing techniques allow for reprogramming of the device, and include techniques for reprogramming the network device directly over the network.
Efforts to upgrade, however, are largely constrained by the processing capabilities of the legacy device. That is, there are some upgrades that require more processing power or memory, or require more electronic circuitry, than originally provided with the legacy device. In such circumstances, it is not possible to provide some upgrades on some machines.
In an effort to address this situation, it has been considered to provide extended functionality and upgrades in an interface device interposed between the networkable device and the network. FIGS. 1A and 1B illustrate this situation in connection with a networkable printer. As shown in FIG. 1A, a legacy printer 10 which is connected to network 11 has constraints on processing power and/or electrical circuitry that make it impossible to provide for upgrades. As shown in FIG. 1B, an interface device 12 is interposed between the network 11 and printer 10. The interface device includes the desired upgrades, and functions to intercept network transmissions to and from printer 10, process such transmissions in accordance with the upgraded functionality, and re-transmit the transmission to printer 10 but in a format understood by the legacy printer. By virtue of the interface device, it is possible to provide for extended and upgraded functionality on printer 10 even when printer 10 is constrained such that the functionality cannot be provided on the printer itself.
FIG. 2 illustrates interface device 12 in greater detail. As shown in FIG. 2, the interface device 12 includes a hub 14 and a circuit board 15 which includes the extended functionality desired for legacy printer 10. The hub 14 includes plural ports including a first port A to which network 11 is connected, a second port B to which printer 10 is connected, and a third port C to which the circuit board is connected. In accordance with standard functionality of the hub, transmissions received on any one port are repeated to all other ports, as depicted in the double headed arrows of FIG. 2.
One problem arises because of the standard functionality of conventional hubs in that network transmissions received from one port are repeated to all other ports. In particular, there are certain circumstances in which it is undesirable for transmissions intended for printer 10 from circuit board 15 on port C also to be repeated to network 11 on port A. One such circumstance relates to situations where extended functionality provided by board 15 is secure printing functionality. In such a situation, the board receives an encrypted print job from the network, decrypts the print job, and transmits the decrypted print job in “clear text” to printer 10. If such transmissions intended only for printer 10 are also repeated to network 11 at port A, the entire network would receive a “clear text” version of potentially sensitive print jobs that were intended only for printer 10.